Mutant BRAF^T1799A can be detected in the blood of papillary thyroid carcinoma patients and correlates with disease status

Context: The BRAF^T1799A transversion is the most frequent morphotype-specific somatic mutation in papillary thyroid carcinoma (PTC). The ability to detect this mutation in the circulation could aid in diagnosis and follow-up of PTC patients. Objective: Our objective was to develop and clinically validate a sensitive and specific assay for the detection of BRAF^T1799A in blood samples from PTC patients. Design: We developed an allele-specific real-time PCR method for the detection of BRAF ^T1799A in blood samples and studied prospectively blood samples from 193 patients with thyroid cancer (173 PTC, 20 non-PTC) attending for routine follow-up. The results of molecular testing were correlated with disease status and thyroglobulin measurements. BRAF^T1799A status of the original tumor samples was also confirmed, where available. Results: The assay had a detection sensitivity of fewer than one heterozygote BRAF^T1799A- carrying cell per 100,000 diploid cells, without detectable cross-reactivity between wild-type BRAF and BRAF^T1799A. Circulating BRAF ^T1799A was detected in 20 of 173 PTC patients and in none of the 20 non-PTC patients. BRAF^T1799A-positive samples contained between one in 326 and fewer than one in 100,000 copies of BRAF^T1799A. Tissue BRAF status correlated with blood BRAF status, whereas BRAF^T1799A positivity in blood correlated with the presence of active disease at the time of the blood draw, with eight of the 38 PTC patients with persistent/recurrent disease being positive for circulating BRAF^T1799A (relative risk vs. circulating BRAF^T1799A-negative, 2.55; P < 0.04). Conclusions: BRAF^T1799A can be detected in the blood of PTC patients with residual or metastatic disease and may provide diagnostic information.